What defines a T-unit?

• A. A sentence with no subordinate clauses
• B. One main clause with all subordinate clauses and nonclausal phrases attached
• C. A clause with a dependent clause only
• D. Any utterance with three or more clauses

Answer: (B)

A T-unit is a single main clause plus any subordinate clauses and nonclausal phrases attached to it. This defines the unit researchers count when analyzing syntactic complexity, such as in MLU analyses, because it centers on one central proposition (the main clause) and everything that attaches to it.

That’s why the best choice describes one main clause with all attached subordinate clauses and nonclausal phrases. It captures both the core clause and the material that attaches to it, which can include adverbials, infinitives, participial phrases, or prepositional phrases. For example, a sentence like “The boy ran quickly because the wind was strong” has one main clause “The boy ran” plus attached pieces “quickly” and the subordinate clause “because the wind was strong,” all part of the same T-unit.

While a sentence with no subordinate clauses is still a valid T-unit in a narrower sense, the full definition emphasizes that a T-unit can include attachments, not just a plain main clause. Likewise, defining a T-unit by the number of clauses or by needing three or more clauses misses the structural idea of a single main clause with attached material.